Injection molding machine



April 3, 1945. Q JOBST 2,372,833

INJECTION, MOLDING MACHINE Filed Feb. 11, 1941 11 Sheets-Sheet 1 INVENTOR Conrad Jbbst,

A1TORN vs April 3, 1945.. v c. JOBST 2,372,833

INJECTION MOLDING MACHINE Filed Feb. 11, 194i 11 Sheets-Sheet s 1BYDMQIY A'ITORNE s April 3, 1945. c. JOBST 2,372,833

INJECTION MOLDING MACHINE 1'1 Sheets-Sheet 5 Filed Feb. 11, 1941 2'" Conrad Jbbst,

3, C. JOBST INJECTION MOLDING MACHINE Filed Feb. 11, 1941 11 Sheets-Sheet e NVENTOR Cour-a dbl-:56,

avg/Z2194 ATTORNE S April 3, 1945.

C. JOBST nmzcnou MOLDING MACHINE Filed Feb. 11, 1941 ll Sheets-Sheet '7 WNW.

' M Conrad (761256, ma

A'FI'ORNE S April 3, 1945. JOBST 2,372,833

INJECTION MOLDING MACHINE Filed Feb. 11, 1941 ll Sheets-Sheet 8 I INVENTOVR Conrad Jbst,

ATTORN s April 1945- v c. JOBST INJECTION MOLDING MACHINE 11 Sheets-Sheet 9 Filed Feb. 11, 1941 INVENTOR Conrad (7211786, BY 6 ATTORNE s April 3, 1945. c. JOBST 2,372,833

INJECTION MOLDING MACHI NE Filed Feb. 11, 1941 lI L Sheets-Sheet l0 INVENTOR Conrad JEzbst,

ATTOR YS A ril 3, I945. Q JQBST 2,372,833

I INJECTIQN MOLDING MACHINE Filed Feb. 11, 1941 11 Sheets-Sheet 11 I INVENTOR' Conrad Jbbst,

BY A

ATTORN is Patented Apr. 3, 1945 UNITED STATES PATENT OFFECE mmo'rron MOIDING momma Conrad rota, Toledo, om application February 11,1941, Serial No. 372,399 29 Claims. (ems-3o) My invention relates .to machines for molding thermoplastic materials and particularly to machines for manufacturing castings or molded articles from organic molding materials of the thermosettlng type, which materials are supplied to the machine in granulated or powdered form,. heat treated to convert them into a plastic condition and injected under pressure into the molds in which the material sets and hardens. I

An object of my invention is to produce a machine which by overcoming various defects and dimculties encountered in prior art machines, is operative to mold articles of superior quality and free from defects incident to prior art methods. In the manufacture of thermoplastic articles by injection methods very high pressures are ordi-' narily employed for injecting the material into the molds and holding the molds closed while the material sets and hardens. Hydraulic mechanism is ordinarily employed for such purpose, the hydraulic pressure being transmitted through toggle mechanisms designed to permit the build ing .up of extremely high pressures. material has been heated and injected in a viscous condition into the mold, there is a certain amount of expansion of the material as it cools. This expansive force is practically irre-v sistible so that enormous pressure is built up within the molds, requiring a correspondingly great hydraulic pressure to be maintained if the molds are to be held closed. With hydraulic operation it has been found impractical or impossible to hold the moldsproperly closed during such expansion of the material. This isdue in part to inherent defects in hydraulic operation. The oil ordinarily used has a creeping power which is not under control and the functioning of the oil is sluggish. The toggle devices where used for locking the mold in closed position are subject to wear and also wear unevenly so that their After the solid unyielding backing for the mold sections by which they are held tightly closed against the highest. pressures developed therein. The inven-- ing material, the molds may be completely filled and the curing and hardening of the material completed without developing the very high pressures which have heretofore been employed and found necessary in practicing prior art methods; A further object of the invention is to provide a machine in which the mold sections may be brought together by means of electric motors cessive pressures to the molds. In prior artmechanisms, particularly in the use of. hydraulic means, the enormously high pressures applied to the mold sections as deemed necessary in attempting to hold the molds properly closed, is destructive of the molds, causing bending ordistortion of the mold sections and wear of the mold faces.

effectiveness for holding the molds tightly closed is quickly reduced. As a result the material as it cools and expands forces the meetingedges of the molds apart, the material being forced out. In order to overcome this flashing, it is customary to keep the temperature down to avoid excessively high pressures from being built up.

This reduced temperature is insufllcient to produce a completely homogeneous and plastic con,-

This difllculty is overcome by the present invention in which the molds are held closed by means of a solid backing without requiring a' high pressure to be applied at ,the meeting faces of the molds.

A further object of my invention is to provide automatic means for protecting the molds in the event of any fragments or pieces of hardened molding material or any other obstructing materials .coming between the mold sections or meeting faces thereof while the mold is being closed. Any such obstructing material coming between the mold faces and subjected to the high pressures ordinarily used, is ruinous to the molds asluch material is embedded in or otherwise mutilatesthemoldhcc. Thisbalprovedtobecseinvention is to overcome this difliculty and to this end there-is provided electro-responsive means for automatically stopping the mold closing motors in the event of any obstructing material interfering with the normal closing movements,

such means operating before an injurious pres- I sure has been developed.

A further object of the invention is to provide improved means for effecting an evendistribution of the molding material in its passage through the heating chamber to the molds, thereby insuring uniform heating of the material. The invention further provides means for insuring all of the particles of molding material being Fig. 21 is a wiring diagram of the electrical equipment.

The framework of the machine comprises vertically disposed parallel plates 25 forming the sides of the frame, a vertically disposed end abutment plate 26 (Fig. 2) at one end of the machine, an inner abutment plate 21 (Fig. 5) and a horizontally disposed tie plate 28 extending lengthwise of the machine between the abutment p1ates.,

The ends of the plate 28 seat on the upper ends of the abutment plates and are bolted thereto by bolts 29. The side plates 25 are attached to said abutment plates and also to the tie plate 28 by maintained in the heating chamber substantially the same length of time while passing therethrough, resulting in uniform heating and a homogeneous condition of the plasticized material.

A further object of the invention is to provide means for preventing heated molding material from mixing with the cold material as it commences its passage through the heating chamber.

Other objects of the invention will appearhereinafter.

Referring to the accompanying drawings which illustrate a machine embodying the principles of my invention:

Fig. 1 is a side elevation of the machine.

Figs. 2 to '7 inclusive together provide a composite view of the machine in sectional elevation, these views when placed side by side in the order of the figure numbers, illustrating substantially the complete machine. Figs. 5, 6 and '7 are sections at the longitudinal center line of the ma- 'naled in the frame 31.

attaching means 30 such as bolts or rivets. The

inner abutment plate 21 has cast integral therea with an extension frame 3i comprising side plates (Figs. 1, 5, 6, 7, 8) and a connecting web 32.

The frame 3! provides a support for a carriage 33 which carries the injector mechanism. The

carriage 33 is mounted for movement lengthwise of the machine, being supported and guided on rails 34 attached to the frame 3|. The injector mechanism as a whole is movable to and from its operative position shown on the drawings, by means of a rack bar bolted to the under side of the carriage and having rack teeth to run in mesh with a pinion 36 keyed to a shaft 31 jour- The shaft is rotated by means of a hand wheel or hand wheels 38 (Fig. 8) keyed to one or both ends of the shaft. This construction permits the injector mechanism to be retracted into a convenient position for making any required changes of parts, repairs, etc.

The injector carriage is normally secured in its operative position by a stop screw (Figs. 1

chine, that is, along the axis of the injector,

while the sections of Figs. 2, 3 and 4 are in a plane offset laterally fromsaid center line to illustrate the mold closing spindle mechanism.

Fig. 3 is a section at the line 3 3 on Fig. 3.

Fig. 5* is a section at the line 5**Ii on Fig. 5.

Fig. 8 is a cross-sectional elevation at the line 8-8 on Fig. 1, illustrating the driving mechanism for the injector plunger.

Fig. 9.-is a section at the line 9-9 on Fig. 1.

Fig. 10 is a section at the line Ill-l0 on Fig. 6.

Fig. 11 is a section at the line IIH on Fig. 5.

Fig. 12 is a section at the line 12-42 on Fig. 1. showing means for feeding molding material to the injector.

Fig. 13 is a section at the line i 3-|3 on Fig. 2, showing gearing connecting the mold closing spindles with their driving motors.

Fig. 14 is a section through the mold carriage at the line l4l4 on Fig. 4.

Fig. 15 is a fragmentary sectional'view of microswitches and their control devices shown in Fig. 1.

Fig. 16 is a section at the line Ii-Ii on Fig. 15.

Fig: 17 is a fragmentary sectional elevation of the injector mechanism and shows particularly the means for rotating the injector plunger.

Fig. 18 is a section at the line i8-I8 on Fig. 1'7.

Fig. 19 is a fragmentary perspective view of the rotary injector plunger.

3|. By rocking the shaft 42 the stop screw may be swung upward from its inoperative position (Fig. 7) into position to engage the outer end of the injector carriage and form a positive means for holding the latter in operative position.

The mold comprises partible mold sections 43 and 44 (Figs. 5, 5 having abutting faces meeting in a vertical plane. The mold sections as shown are formed with a multiplicity of mold cavities 45. The molding material is injected into the molds'through an injector nozzle which opens into a manifold channel or sprue 46 having branch openings into the mold cavities. The mold section 44 is mounted on the abutment plate 21. A platen 41 interposed between the mold section and the plate 21 provides a backing for the mold, the parts being removably attached to the plate 21 by screw bolts 48. The plunger tip or nose 4!! (Fig. 20) projects through a bushing 48 in the platen 41 and the forward end of the tip abuts a plate 48 inset in the mold section 44.

The mold section 43 is carried on a mold carriage 50 (see Figs. 3, 4 and 14) mounted for reciprocating movement lengthwise of the machine. Bearings for the mold carriage comprise the bearing balls 5| which run on tracks or raceways 52 mounted respectively on the tie plate 28 and the carriage 50. The bearing balls are held in position by spacing strips or cages 53. The mold carriage is reciprocated by means of motor driven screw-threaded shafts 54, herein referred to as drive shafts or spindles. These have screwthreaded connections with internally threaded sleeves or nuts 55 mounted in cylinders 58 aligned Fig. 20 is a. fragmentary sectional view showing the tip of the injector nozzle, expansion control devices and means for ejecting articles from the mold.

with the screw shafts. These cylinders are formed integral with a vertical face plate 51 (Figs. 4 and 5) ofthe mold carriage. The mold section 43 is backed by a platen II which in turn abuts a plate 59 bearing against the face of the The latter isformed to provide housings for the shaft couplings 62 and together with the abutment plate 26 provides a housing forthe shafts 63- and gearing driven thereby. Each shaft 63 is formed with a driving pinion 66, which pinions mesh with spur gears 6.1 mounted to rotate freely on bushings 68 in which the spindles 54 are journaled. A driving connection between each spindle 54 and its driving gear 61 includes a lug 69 on the gear 61 and a lug in formed on a hub or sleeve 'Il secured to, the end of the spindle shaft 54.

As shown, there are four driving spindles so arranged that the driving force of each spindle is applied in a direction perpendicular to the mold plate. and adjacent one corner thereof. In this manner there is a substantially uniform mold closing pressure applied throughout the area of the mold plate. When the motors are driven in a forward direction and the mold thereby closed, the motors are brought to rest. The current is not cut off from the motors when the mold closes, but electrical resistance is introduced into the by an. electric motor 99. A conventional vibrator 83* (Fig; 1) delivers thev molding material in termittently in measured charges to the chute 84.

The molding material is fed forward through the passageway I9 to the mold and. compacted within the mold by means of a tubular injector plunger 90 (Figs. 6, 17, 18, 19) whichsurrounds the inner spindle I5 and is reciprocated lengthwise within the annular passageway I8. The

mechanism for reciprocating the plunger is as fol- IOWSZ An electric motor I (Figs. 1, 8) has, herein referredto as the injection motor, driving connection through a coupling 92 with a worm shaft 93 on which is a worm running in mesh with a worm gear wheel 94 (Figs. 7 and 8) joumaled in the injector carriage for rotation about the axis of the injector spindle. The worm gear has driving connection with a thrust driving mechanism comprising an inner tubular shaft 96 and an outer tubular shaft 91. The shaft 96 is screwthreaded or provided on its outer surface with a spiral groove to receive thrust bearing balls 98 which also run in corresponding spiral grooves in the inner surface of the shaft 91. The worm gear 94 is keyed to the shaft 91 for rotating it by means of keys 99. The bearing balls 98 are held motor circuits so that a driving force is maintained at a reduced torque, all as hereinafter set forth. This serves to positively prevent any backward or opening movement of the mold because any pressure built up therein, no matter how great, would be insufilcient to drive the spindles backward against the torque of the motors. The abutment plate 26 provides with the screw spin.- dles and mold carriage a solid abutment so that there can be no backward movement of the mold section without compressing the metal. Thrust bearings 12 (Fig. 2) are interposed between the abutment plate and flanges I3 on the spindles to take the end thrust of the spindles.

The injector mechanism includes an inner tubular shaft or spindle I5 (Figs. 6, 7 and 17) mounted in the carriage 33 and held against lengthwise movement-by annular ribs 16*- formed thereon and engaging corresponding grooves in a cap block 16 (Figs. '7, 9) bolted to the carriage. This spindle is made in two sections connected by a connecting ring 'II having outer and inner screw-threaded engagement with said sections regether by screw bolts 83. The molding material in granular or powdered form is fed throu h a chute 84 into a tower 96 bolted to the block 80.

The material is fed or forced from the tower through an opening in the bushing 8|, into the passageway I9 by means of a paddle wheel or propeller 81 on the lower end of a shaft 86 extending upwardly through the tower and driven material to enter the passageway I8.

in place by a cage I60. The rear end of the plunger. abuts the forward end of the shaft '96 which drives the plunger forward. The plunger is connected to the shaft to be retracted thereby, by means of a flanged collar IOI threaded onto said shaft. The construction is such that the plunger 90 is rotatable independently of the shaft 96 and relative thereto by means hereinafter described. Y

. The thrust shaft 96 is held against rotation by means of a bushing I02 (Figs. '7 and 8) keyed tothe carriage block and formed with ribs having a slidable connection with the shaft. Rotation of the worm gear 94 and the shaft 91 therewith operates through the thrust bearings to impart lengthwise. movement to the shaft 96 for reciprocating the injector plunger 90. Thrust bearings I03 take up the thrust or back pressure of the tube 91 as the injector plunger is. moved forward.

When the plunger 90 is fully retracted, the forward end thereof is moved back beyond the lower, open end of the tower 86, permitting the molding When the plunger moves forward, the material is forced through the passageway to the mold. In order to obtain a uniform distribution of the material throughout the circumference of the passageway I9, provision is made for rotating the plunger. The means for effecting such rotation includes a motor I 04 (Fig. 6) operating through bevel gearing I05 to rotate a shaft I 06 (Figs. 1'7, 18) having a bearing in the forward end of the tubular shaft 96. A pinion I01, splined on the shaft I06, runs in mesh with an annular gear I06 formed on the outer end of the plunger 90. The spline connection of the shaft I06 and gear III'I permits the gear to slide along the shaft as, the thrust driving shaft 96 is reciprocated. The front end surface of the plunger 90 is formed with corrugations or teeth I09 (Fig. 19) which as the plunger rotates insurer a proper distribution of the molding material within the channel I6 and cause more or less of a circular movement of the ma rality of sets of electrical heating elements. These include a front set H and a rear set III. (Figs. and 6) both mounted in openings in the forward section of the inner spindle I5. .Surrounding the outer spindle shaft I9 are additional sets of heating elements including a rear set II2, an intermediate set H3, and a front set II4.

Each of said sets of heaters may be arranged in.

In order to localize the heating operation, control the temperature of the plunger 90, and prevent heating of the material until brought into th zone of the heating elements, cooling means is provided for circulating a cooling fluid within the irmer tubular spindle I5. Such cooling means comprises concentric sheet metal tubes IIB (Figs. 6, 7, 1'7) extending lengthwise through the spindle and defining a tubular passageway opening at its inner end into a cooling chamber II'I. Baflles III (Fig. 12) are provided to direct the circulation of fluid within said chamber.

Additional cooling means designed particularly to prevent heat from the electrical heating elements being' transmitted'to the molding material before the latter is moved forward through the channel I8, comprises a system for circulating a cooling fluid through the flanged end (i (Figs. 6 and of the bushing 8|. The cooling fluid is admitted through a pipe I Iii to an annular passageway I I5 through which it is conducted, and

' thence through an opening I I6 to an inner annular channel IIIi and through the latter to a discharge pipe H5.

An electrical board I I8 (Fig. 1) is provided with indicators II9 individual to the groups of heating elements, and adjusting devices I whereby the heaters may be set for maintaining desired temperatures. A potentiometer point I2I is located at the forward end of the injector to indicate the temperature where the material enters the mold. Another potentiometer I22- (Fig. 5) is located adjacent the heater elements IIO, indicating the temperature at a point more remote from the mold. Still other potentiometers may be placed at convenient positions to indicate temperatures at any desired points within the heating zone.

Referring to Figs. 3 and 3, I have provided safety mechanism for limiting the mold closing pressure applied to the molds in the event of any obstructing material coming between the mold faces or interfering with normal closing of the mold. Such mechanism includes spring means by which the forward movement of one or more of the spindles 54 is transmitted to the cylinder 56.

As shown in Figs. 3 and 3, an upper spindle 54 is equipped with such spring means. This includes an annular series of coil springs I23 which are thereby compressing the springs.

against which the flange I24 abuts when the sleeve 55 is retracted. During the normal mold closing movement the pressure of the flange I24 against the springs is insufficient to compress them until the mold sections are brought together. The continued rotation of the spindle 54 then serves to move the threaded sleeve 55 forward relative to the carriage as shown in Fig. 3,

Keys I29 attached to the threaded sleeve 55 prevent rotation of the sleeve within the tube 55 and also limit the forward movement of said sleeve.

During th compression of the springs I23 a Micro-switch I30 is actuated by an arm III attached to the sleeve 55. This serves to start the injector motor as hereinafter set forth. A second Micro-switch I32 is adapted to be operated by the arm I3I and functions as a safety switch in the event of an obstruction interfering with the normal closing of the mold. The switch I32 is moved to closed position during the compression of the springs as the sleeve 55 is advanced after the carriage 50 has been arrested by such an obstruction. The switch I32 when thus closed operates through a relay to throw the reversing switch for the motors M and cause the mold carriage to be withdrawn as pointed out hereinafter. The circuit for the switch I32 is opened by the closing movement of the mold so that the switch is ineffective when operated by the arm I3I when' the mold is closed normally.

Referring to Figs. 1, 15 and 16, a series of 1 Micro-switches I33, I34 and I35 are mounted on the machine frame and are operated by cams on the mold carriage for controlling various operations of the machine as will be described later. The switch I33 (see Figs. 15, 16) is actuated by a plunger I35 operating through means including an arm I31. The plunger in turn is actuated by a cam I38 mounted for adjustment on a supporting block I39 which in turn is adjustably mounted in a supporting bar or bracket I40 (Figs. 14, 15) attached to the mold carriage 50. The switch I33 is opened by its cam as the mold is closed. The functions of the switch I33 will.

appear more fully later. The switch I34 is actuated by a cam HI, and serves to introduce resistance into the field circuit of the motors M as hereinafter described. The switch I35 is actuated by a cam I42 as-the carriage is retracted to stop the motors.

Switch mechanism is provided as shown in Figs. 4 and 4, which is actuated by the back pressure of the molding material when the molds are filled for controlling various operations as hereinafter described. Such mechanism includes a rod I43 mounted for-a very limited lengthwise movement in the mold carriage. The latter is formed with a tubular casing I44 in which is a sleeve I45 attached thereto by screws I45. A

screw-threaded plug I41 mounted in said sleeve is adjustable therein for adjusting the compression of a coil spring I49 housed within the sleeve and held under compression between the plug and a head I48 on the rod I43, which head limits the forward movement of the rod. A collar I threaded on the head I48 permits a very limited backward movement of the rod. An arm I5I attached to the rod I43 provides an operatingconnection between said rod and a Micro-switch I52 mounted on a. support I53. The switch I52 is actuated, by means to be described, when a predetermined'pressure of the molding material has been built up within the mold by the injector plunger 90, and operates various electrical con-' trolling devices as pointed out hereinafter.

Referring to Fig.7, a switch operating bar I54 iector plunger was retracted during the preceding cycle of operations. The switch I58 is so constructed that it may be operated by the magnet coil I88 regardless of the position of the rod I54. Closing of the switch I58 establishes a circuit for the field windings of the injector motor I so that the latter is started in a forward direction, it being noted that the from the mold 43 as the mold carriage is retracted, by ejector rods I55 and I56 (Figs. 1, 2, 3, 4, 13, 14) mounted on the machine frame. The middle rod I56 is in line with a rod l51 (Fig. 4 which is mounted to move freely lengthwise through the tubular rod I43. The rod I51 is pushed forward by the rod I55 and operates through a rod I 14 (Fig. 5) hereinafter described, to eject the molded articles. The rods I55 are arranged to engage a plate I58 (Figs. 1 and 5) and move the latter forward, thereby actuatin ejector devices I58".

Referring to Fig. 21, the electric motors and controlling devices are actuated by current from the mains a, b, c of a three-phase system. The

switch I59 in circuit with the field coils of the J motors. This field circuit may be traced from the switch I59 through a conductor I60, switch I33, conductor I8I, leads I62, through the motors and conductor I53 back to the switch I59. (The switch I in parallel with the switch I59 is at this time open.) A circuit for the rotors of the motors may be traced from the main b through conductor I64, reversing switch I65 (which at this time is in the dotted line position), conductor I55, to and through the motor windings and return wire I61 to main a. The motors M being thus energized drive the mold carriage in a forward direction. As the'carriage commences its forward movement the switch I35 (Fig. 15) is actuated as its operating plunger runs off the cam M2, thus closing the switch as shown in Fig. 2 1 and by-passing the switch I59 so .that the motor circuit is maintained after the push buttom switch is released. As the mold carriagenears the limit of its forward move-- ment, the switch I 30 (Figs, 15, 21)' is opened by its cam- MI and introducesan impedance I3 4 into the motor circuit, thereby reducing the torque of the motors M. The-motors are stopped by theresistance of the driving spindles 53 as the molds close but remain energized and apply a driving force which prevents any possible opening movement of the molds.

As the mold carriage reaches its forward position with the moldclosed, the continued rotation of the spindle 54 (Fig. 3) causes the arm I3I to engage and close the switch I38 whilethe springs I23 are being compressed. Closing of the switch I30 establishes a circuit for a magnet coil I68, which circuit may be traced from themain 1) through conductor I59,-switch- I30, coil I68, and wires I10 and I12 to the main 0. At the time the switch I30 is actuated .the rightof-way switch I33 is in open-position, having been opened by its cam I38 (Figs. 1, 1 5, 16, 21) as the mold completes its closing movement.

- The coil I68 being thus energized by closing of the switch I30, closes the return limit switch I58 which was opened by .the rod I54 when the in-.

opened, introduces a resistance I55 into the motor circuit, reducing the torque andslowing down the motor. As the mold is filled the back pressure of the molding material stalls the motor but the'motor circuits remain closed during the cooling and setting of the molding material so that the torque of the motor prevents any retraction of the plunger. when the switch I55 is opened, a switch I55 (Fig. 21) which may be I mechanically connected thereto, is also opened and cuts oil the current from the motor I04 so that the rotation of theplunger is discontinued until the switch I55 is again closed.

As the mold is filled the increasing pressure built up therein operates the Micro-switch I52 through the following mechanism. The rod I14 (Fig. 5) is mounted centrally of the mold for lengthwise movement and projects forward to the mold cavity and is thus subiected to an end pressure by the molding material. The rod is formed with a head I15 which is slidable in the plate 59 and arranged to abut the front-face of the head I 58 (Figs. 4a.,and 5). A coil spring I10 holds the rod I14 in said position. when a certain pressure has been built up within the mold, the rod I13 is moved lengthwise thereby and moves the rod I43 in oppwtion to the pressure of the spring I59 and thus 'actuates the Micro-switch I52. Adjustment of the plug I51 adiustably varies the amount of pressure of the molding material required to actuate the switch.

Referring now to Fig. 21, when the switch I52 is operated by the pressure of the molding material, a circuit is completed which may be traced from the main b through wires I39, I11, magnet coil I13 of a timer switch I15, wire I80, switch I52, holding coil lBI for switch I52, wire I82, switch I83, coil I35 of a timer switch I85, wire I83 to line wire 0. As the closing of the switch I52 establishes a circuit through its magnet coil I8I, said switch is held closed. The coil I18 for the timer switch I19 being energized operates-to close the switch after a predetemiinedtime limit, thereby establishing a circuit for the coil I81 of the reversing switch I13 for the injector motor. The switch I13 is thus reversed and reverses the mo-. tor I so that the injector plunger is retracted. As the closing of the switch I52 also energizes the timer coil I84, the timer switch. I85 15 also closed after a predetermined'time limit. Closing of the switch I85 energizes the coil I88 which operates the reversing switch I6-5for the motors M. The circuit for the coil I88 may be traced from the-main I) through conductors I89, I11,

and I19 respectively, also the magnet coil I8I of the switch I52. The relay switches and the switch I52 are thereby opened. The opening of these switches effects the operation of the reversing switches I65 and I13 preparatory to the succeeding cycle of operations.

The operation of the safety mechanism when any foreign material gets between the mold faces or obstructs the closing movement of the molds is as follows:

Such obstruction by resisting the forward movement ,of the mold carriage causes a compression of the springs I23 (Fig. 3) and actuates the switch I32. This may take place when a pressure of 100 or 200 lbs., for example, has been built up which is insufficient to injure the molds. This establishes a circuit which may be traced from the main line b through the switch I32, wire I92, switch I33, wire I92, magnet coil I93 of a switch I94, wires I95'and I86 to line wire 0. The switch I94 is now closed and completes a circuit for the coil I88 of the reversing switch I65. This circuit may be traced from the main line 0 through conductors I86, I9I, coil I88, wire I91, switch I94, and conductors I98, I69, to main line b. The reversing switch I65 is therefore operated and reverses the motors M so that, the mold carriage is withdrawn. The switch I32 is positioned to be actuated by the contact plate I3I before the-latter reaches the switch I30, so that the switch I32 can effect the reversal of the motors M without operating the switch I30 which controls the injection motor I. The safety switch I32 can onlyfunction while the mold is in open position because theright-of-way switch I33 is opened as the mold closes. The switch cam I38 may be adjusted to open the switch I33, for example, when the mold faces are within two or three thousandths of an inch apart.

The means for-automatically controlling and limiting the pressure built up in the mold by the expansion of the molding material comprises pressure relief elements 200 (Fig. 20) in the form of short headed pins or studs mounted in the plate 48. The pins extend freely through said plate and' their forward ends are flush with the surface of the mold wall. The pins are yleldingly held in this position by coil springs 202, the compression of which may be adjusted by screw-threaded plugs 203. When the pressure of the molding material reaches a predetermined limit due to expansion, the holding pressure of the springs is overbalanced so that the pins 200 recede to make room for the expanding material.

Modifications may be resorted to within the spirit and scope of the appended claims.

I claim:

1.'A molding machine comprising a mold, in

jecting mechanism for injecting a molten plast c molding material into the mold, said mechanism including means providing a restricted passageway opening into the mold, a plunger for forcing the molding material through said passageway, means for driving'said plunger and thereby forcmeans operable by back pressure built up within the mold when the mold cavity is filled to reduce the driving force applied to said plunger, and means independent of said lunger for automatically regulating the pressure within the mold and preventing excess pressure due to expansion of the molding material during cooling and setting thereof. 1

2. A molding machine comprising a mold, injecting mechanism for injecting a molten plastic molding material into the mold, said mechanism including means providing a restricted passageway opening into the mold, a plunger for forcing the molding material through said passageway, means for driving said'plunger and thereby forcing the molding material-into the mold, said plunger driving means including an electric motor, and automatic means separate from said plunger and operable independently thereof by back pressure developed in the mold after the latter is filled to reduce the torque of the motor and. thereby reduce the force applied to the plunger.

3. An injection molding. machinecomprising a mold including partible mold sections, one of said sections being mounted for movement to and from the other section for closing and opening the mold, an electric motor, a screw-threaded shaft operatively connected to and driven by the motor, said shaft extending in the direction of said movement of the mold section, a nut threaded on said shaft and connected to the movable mold section for moving the latter, when the motor is operated, electro-responsive means operable automatically to introduce a resistance into a circuit of the motor as the movable mold section approaches mold closing position and thereby causing the motor to operate with a reduced driving torque applied to said shaft during the final closing movement of the mold section and thereafter holding the mold closed, and means for in- .lecting molding material into the mold and building up a pressure therein while the mold is held closed under said reduced driving-torque.

4. An injection molding machine comprising partible mold sections including a section having a stationary mounting and a movable section, a carriage on which said movable section is mounted, said carriage being mounted for reciprocating movement for moving said movable section to and from a mold closing position, a plurality of parallel screw shafts extending in the direction of said movement of the carriage, means for rotating the shafts, nuts threaded on said shafts and connected to the carriage, means providing a yielding connection between one of said nuts and the mold carriage by which a continued rotation of the associated shaft is permitted after the movable mold section is brought to mold closing position, aninjection motor, and ele'c'tro-responsive means operable by said nut during said continued movement to establish a circuit for said motor.

5. A molding machine comprising a framework ing molding material into the mold, automatic 7 abutment and extending in the direction of movement of the carriage, said shafts being symmetritween the motors and shafts, means providing a yielding connection between one of said nuts and the carriage, permitting a limited continued movement'of the said one nut by its driving shaft after the mold is. closed, an injection motor, and electro-responsive means actuated by the nut during said limited-movement to effect the operation of said injection motor.

6. A molding machine comprising a framework including spaced abutments, a partible mold comprising a mold section mountedon and backed by one said abutment, a carriage on which the other mold section is supported, said carriage mounted between said abutments for reciprocation by which the mold section thereon is movable to and from a mold closing position, driving means for the carriage interposed between the carriage and the other said abutment, said driving means including a plurality of parallel screw-threaded shafts journalled in said last mentioned abutment and extending in the direction of movement of the carriage, nuts carried on said carriage and in which the shafts are threaded, electric motors individual to said shafts, gearing providing driving connection between the motors and shafts, means providing a yielding connection between one of said nuts and the carriage, permitting a' limited continued movement of the said one nut by its driving shaft after the, mold is closed, an injection motor, an injection plunger driven thereby,,electro-responsive means actuated by the nut during said limited movement to establish a circuit for the injection motor and causeit to drive said plunger, and means to introduce an impedance into the injection motor circuit by which the driving torque'of the motor is reduced, permitting a reduced driving torque to be applied to the injection plunger and maintained after the injection motor is brought to rest.

7. A molding machine comprising separable mold sections, an electric motor, mechanism providing a driving connection between the motor and a mold section for moving the latter to and from mold closing position, said mechanism including a yieldable element permitting continued operation of the motor independently of movement of the mold section toward its closed position in the event of an obstruction offering ab.

normal resistance to the mold closing movement, electro-responsive means operated by said element to control and stop the motor, and automatic mechanism for preventing the operation of said last mentioned means while the mold is closed.

riage to mold closing position. said springs oflering a resistance to compression sufllcient to permit normal closing of the mold without relative movement of said nut and carriage and yieldable under an abnormal resistance to the mold closing movement of the carriage, thereby permitting a forward movement of the nut relative to the carriage when there is an obstruction between the mold sections, and electro-responsive means actuated by said nut during said relative movement for controlling and stopping themoto'r.

9. An injection molding machine comprising a mold, an injector comprising a heating chamber, the latter providing an annular passageway having a forward end portion converging into a re-- stricted outlet which opens into the mold cavity,

means for introducing charges of molding material into said chamber, a tubular plunger, means for moving the plunger forward in said passageway and thereby forcing the material into the mold, and means for rotating. the plunger during its forward movement and thereby distributing the material circumferentially within said pas-- sageway, the forward end of the plunger being provided with projectionsto engage and insure an effective distribution of the molding material.

10. A molding machine comprising a mold,

' means for-introducing a'plastic' molding material into the mold and building "up a predetermined pressure within the mold,- a wall of the mold being provided with a restricted passageway leading from themold cavity to receive excess material, automatic means cooperating with said passageway to prevent excess pressure being built up within the mold by expansion of the molding material therein, said automatic means comprising an element movable in said passageway toward the mold cavity, a stop positioned and arranged to limit said movement and prevent said element from entering the mold cavity, a spring held under compression and holding said element against the stop while the mold cavity is being filled and a predetermined normal pressure is built up therein and permitting retractive movement of said element when said normal pressure 'is exceeded, and adjusting mechanism for adjust- 8. A molding machine comprising a mold hav- 7 driving force is transmitted for moving 'the caring the compression of said spring and thereby adjustably varying the amount of pressure required toretract said element, whereby the maximum degree of pressure built up within the mold may be adjustably varied. t

11. A molding machine comprising a mold having a mold cavity, means for introducing a plastic material into the mold and filling the mold cav-.

ity, pressure controlling means comprising a pressure relief element, the mold being formed with a restricted passageway leading'from the mold cavity and in which said element is mounted for movement toward and from the mold cavity, means for holding said element ina position exterior to the mold cavity throughout the filling of the mold cavity, yielding means providing a backing for said element and permitting the latter to recede after the mold cavity is filled and when a predetermined pressure is developed with- -inthe mold-and adjusting means for adjustably varying the pressure at which said-element will yield under the pressure developed within the mold,

thereby causing a uniform distribution of the V material circumferentially within said passageway.

13, An injection molding machine comprising a mold, an injection nozzle formed with an annular passageway extending therealong, the forward end portion of said passageway being tapered and converging into a restricted opening extending to the mold cavity, meansfor supplying molding material to said passageway, a plunger in said passageway, means for moving the plunger toward the mold and thereby forcing said material into the mold cavit and means for'rotating the plunger while it is moving toward the mold and thereby causing a'uniform distribution of the material circumferentially within said passageway, the forward end of the plunger being provided with means for imparting a rotative movement to the molding material.

14. An injection moldingmachine comprising a mold, an injection nozzle formed with an annular passageway extending therealong, the forward end portion of said passageway being tapered and converging into a restricted opening extending to the mold cavity, means for supplying molding material to said passageway, a plunger in said passageway, means for moving the plunger toward the mold and thereby forcing said material into the mold cavity, means for rotating the plunger while it is moving toward the mold and thereby causing a uniform distribution of the material circumferentially within said passageway, and heating means enveloping said passageway whereby the latter serves as a heat chamber within which the molding material is heated and itively limit the movement of said element.-to-

ward the mold cavity and hold it outside of the mold cavity, a spring providing a backing for said element and holding it in its forward position while the molding material is injected and fills the mold cavity, said pressure relief element being movable backward against the force of said spring by the molding material when a predetermined pressure is built, up within the mold and thereby providing for expansion for the moldin material and regulation of said built-up pressure.

16. An injection molding machine comprising a mold having a mold cavity, means for injecting plastic molding material into the mold and filling the mold cavity, an electric motor for driving the injecting means, a pressure operated device separate from the injecting means and positioned and arranged to contact with the molding material in' the mold, said device being movable under pressure applied thereto by the molding material when the mold has been filled and the pressure built up. to a predetermined degree, spring means providing a backing for said device and opposing said retracting movement, a switch operated by said device when the latter is retracted, and elec tro-responslve means controlled by said switch for reducing the driving force of the motor when the switch is operated.

17. A molding machine comprising a mold having a mold cavity, injecting mechanism for injecting a molten plastic molding material into the mold cavity, said mechanism including means providing a restricted passageway opening into the mold cavity, a plunger for forcing the molding material through said passageway, an electric motor operatively connected to drive said plunger and thereby force molding material into the mold, a pressure regulating device separate from said plunger and positioned tocontact with the molding material in the mold and mounted for retractive movement, spring means providing a backing for said device and opposing such movement, said device being retractable by a predetermined pressure of the molding material, and electro-responsive means actuated by said device for controlling a circuit of the motor and reducing the torque of the motor applied to said plunger.

18. An injection molding machine comprising a mold having separable sections, means for relatively moving said sections to and from, a position in which the mold faces meet'and thereby closing and opening the mold, said means including a screw-threaded shaft, an electric motor connected to rotate said shaft, means forming a driving connection between said screw shaft and a section of the mold for moving said section to, mold closing position, automatic means brought into operation when the mold section reaches a predetermined position as it approaches mold closing position to reduce the forward driving torque of the motor and maintaina reduced driving torque during a predetermined final portion of the mold closing movement and after the motor has stopped for holding the mold closed, and means for injecting molding material into ,the mold and building up a pressure therein while the mold is held closed under said reduced driving torque.

19. An injection molding machine comprising partible mold sections including a section'having a stationary mounting and a movable section, a

carriage on which said movable section is mounted, said carriage being mounted for reciprocating movement for moving said movable section to and from a mold closing position, a plurality of parallel screw shafts having a stationary mounting 1 and extendin in the direction of said movement of the carriage, nuts threaded on said shafts and connected to the carriage, electric motors individual to said shafts, gearing connecting the motors to the respective shafts, said shafts being symmetrically arranged about the axis of the mold tov impart a uniformly distributed driving pressure to the mold sections, electro-responsive means operable automatically as the mold is closed to reduce the driving torque of said motors, and means for injecting a plastic molding material into the mold andbuilding up a prcdeter-' partible mold including a stationary secticn mounted on the face of said forward abutment, and a mold section movable to andfrom said stationary section for closing and opening the mold, a carriage on which said movable section is mounted, said carriage being mounted on saidtegrally therewith, said cylinders being symmetri cally arranged about the axis of the mold and extending rearwardly from said faceplate, screwthreaded nuts carried at the outer ends of said cylinders, screw shafts threaded through said nuts and extending into said cylinders, said shafts being iournalled in said rear abutment, thrust bearings interposed between said shafts and said rear abutments, and means for rotating said shafts.

21. A molding machine comprising partible mold sections having meeting'f aces, means comprising a power motor for moving one section toward the other and thereby closing the mold, and safety means operable by said motor when a predetermined abnormal resistance to the mold closing movement of the moving mold section is ena pressure equal to said holding pressure from being built up in the event of obstructing material between the mold sectionsrinterfering with the normal closing of the mold, and automatic means brought into operation during the final closing movement of the mold for rendering said safety'means ineiiective and thereby permitting said holding pressure to be built up while the mold is closed;

25. An injection molding machine comprising a mold including sections relatively movable to and from each other for closing and opening the mold, a motor, mechanism for transmitting mov tion from the motor to a mold section for closin the mold. and applying a holding pressure to the mold, and electro-responsive means operated au:

normal resistance is offered to such movement,

countered to deenergize said motor before the mold closing movement is completed, and automatic means for preventing the operation of said safety means while the mold is closed.

22. A molding machine comprising sections relatively movable to and from each other for closing and opening the mold, an electric motor, power transmittin mechanism providing driving connections between the motor and a mold section for moving the latter to mold closing position, said mechanism including a movable element and a compression spring permitting said movable mold section to be arrested by a predetermined resistance to its normal closing movement while said element continues its movement against the compressive force of the spring, and an electro-responsive device controlling the motor and arranged to be operated by said element during said continued movement and thereby cut oil the driving power of the. motor, and automatic means brought into operation by the-final closing movement of said movable mold section for rendering said electro-responsive device ineffective.

23. An injection molding machine comprising a mold, injection mechanism for injecting 9. molten plastic molding material into the mold including an injection plunger, a motor for driving the said electro-r'esponsive means being operable to cut oil the driving power of the motor and thereby stop the motor and prevent an objectionable mold closing pressure being applied to the mold,

and means brought into. operation during the final closing movement of the mold to render said electro-responsive means inoperative to control the motor.

26. A molding machine comprising partible mold sections, a power motor, means driven thereplunger, a pressure operated device independent of the plunger and mounted in position to be operated by pressure of the molten plastic within the ing the mold, a power driven mptor, means providing driving connections between the motor and said movable mold section for closing the mold and building up a holding pressure, said driving connections, including safety means through which pressure is applied to the movable mold section, said safety means being operable by-a predetermined back pressure of the movable mold section to out off the driving power from the motor and stop the motor, and thereby prevent,

by for relatively moving said sections for closing and opening the mold and for holding the mold closed, safety means operable automatically by a predetermined pressure applied thereto, said safety means being arranged to receive the back pressure of a mold section caused by a predetermined resistance to the closing movement thereof before the normal closing movement is -completed, saidsafety means being operable to cut oil the power and thereby prevent the application I of excessive pressure to-the mold sections when an obstruction betweenthe mold sections interfers spring between said element and the movable section of the mold, said spring being compressible under pressure developed when an obstruction to the closing movement of the mold oilers an abnormal resistance to such movement, means arranged to be operated by the movement of said movable element during said compression of the spring to cut off the driving power from the motor and thereby prevent excessive pressure between i the mold sections, and auto'maticmeans by which the final closing movement of the mold takes the motor out of the control of said movable element.

28. A molding machinecomprising a sectional mold, one section of the mold being movable toward and from the other for closing and opening the mold, a motor operatively connected to said movable section, and safety means operable when an obstruction is interposed between the mold sections for automatically preventing a normal mold closing pressure from being applied to the movable section, said safety means including a 

